Research On 3D Printing Manufacturing And Performance Of Prefabricated HSFC Pavement Slab

With the promotion of national strategy—"country with strong transportation"and"carbon peaking and carbon neutrality",the new prefabricated pavement materials and the new intelligent manufacturing technologies for the highway project has important theoretical significance and engineering application value.In view of the industrial pain point problem that the existing disposal methods of temporary construction roads lead to a large amount of waste of construction materials and the solid waste generated from demolition pollutes the environment.From both material and member,the 3D printing manufacturing method and the performance research of prefabricated HSFC(High strength fiber concrete)pavement slabs(name as 3D―HSFC)are carried out innovatively.Both new method and new technology of recyclable and reused concrete pavement slabs used in temporary road are developed,and an innovative way for the intelligent construction of Chinese highway engineering is provided as well.The main research contents and results are as follows:(1)The influencing factors,rules and driving mechanism of steel fiber orientation of 3D―HSFC were determined.The influencing rules of screw,nozzle,printing process and material parameters on steel fiber orientation were studied through experiment.The results revealed that the steel fiber orientation was improved with the increase of steel fiber length and content,whereas reduced with the increase of nozzle diameters;The degree of steel fiber orientation was basically about 33%after the 3D―HSFC extruded by the screw;The impact of steel fiber length and content on the steel fiber orientation occurred in the nozzle area during 3D printing.The kinetic mechanism of the steel fiber orientation was analyzed by using smooth particle hydrodynamics(SPH)method.The results showed that the velocity gradient in the 3D―HSFC movement in the nozzle was the driving force of steel fiber orientation.A calculation model of the steel fiber orientation degree with nozzle diameter,steel fiber length and steel fiber content was established.(2)The rule of both printing path and bending direction on the flexural-tensile strength of 3D―HSFC was illustrated.The factors of 3D―HSFC flexural strength were studied by the discrete element numerical model.The results showed that the flexural strength of 3D―HSFC was mainly affected by the angle between printing strips(θ)and the angle between strip and bending direction(φ):whenθincreased from 0°to 90°,the relationship between flexural strength andφwas symmetric withφ=90°,and whenφincreased from 0°to 90°,the relationship between flexural strength andθwas symmetric withθ=90°.The maximum flexural strength was atφ=0°(or 180°),and decreased with increasingθwithin 0°～90°.The minimum flexural strength was atφ=90°,and increased with increasingθwithin 0°～90°.Whenθ=90°,the least difference of flexural strength of 3D-HSFC under loading in all directions(φ=0°～360°)was gotten.A calculation model,which depicted the relationship of the flexural strength,θandφof 3D―HSFC,was established.(3)The factors and rules of the mechanical properties and durability of 3D―HSFC were determined.The mechanical properties such as flexural-tensile strength,compressive strength,splitting tensile strength and bending fatigue,as well as the durability including surface water permeability,salinity resistance and hardened pore structure,were studied from the four aspects of steel fiber orientation,steel fiber length,steel fiber content and printing strip thickness.The results showed that:1)With restriction effect caused by steel fiber,the flexural-tensile strength and splitting tensile strength of 3D―HSFC increased with the increase of steel fiber orientation,steel fiber length and steel fiber content,whereas was little affected by the change of printing strip thickness.On the contrary,the flexural-tensile strength and splitting tensile strength of 3D―HSFC were little affected by the changes of the four factors;2)The compressive strength of 3D―HSFC improved with the increase of steel fiber length and content,whereas was little affected by changes in steel fiber orientation and strip thickness;3)The strength anisotropy index of 3D―HSFC was significantly higher than that of 3D printed cement material without steel fiber,and it gradually increased with the increase of steel fiber length and content;4)Under the same stress ratio,the bending fatigue life of3D―HSFC trabecular beam gradually increased with the increase of steel fiber characteristic parameters(ρ_fl_f/d_f);5)The experiment of surface water permeability and salinity resistance showed that 3D―HSFC had excellent durability performance,and was little affected by the change of steel fiber orientation,steel fiber length,steel fiber content and printing strip thickness.(4)The engineering application performance of 3D―HSFC pavement slab was clarified.The stress levels of different positions at the bottom of 3D―HSFC pavement slabs were determined by an experiment of temporary road engineering.The calculation formula for the minimum thickness of the 3D―HSFC pavement slab under the target fatigue life was established based on the discrete element simulation method.With monitoring at the engineering site,it found that the bottom stress ratio and its growth rate of the 14.4cm thick 3D―HSFC pavement slabs were lower than those of the24cm thick C40 concrete pavement slabs;After being rolled 95200 times by heavy load vehicles,the appearance of 3D―HSFC pavement slabs had no obvious defects,whereas C40 concrete pavement slabs emerged phenomenon of lack of edges and corners.Compared with the C40 concrete pavement slabs,the 3D―HSFC pavement slabs can reduce the volume by 40%,the weight by 35%and the target fatigue life increase to 4.07 times,with excellent recyclable performance.